[en] We describe the intrinsic mechanism of 2-dimensional electron confinement at the n-type
SrTiO3=LaAlO3 interface as a function of the sheet carrier density ns via advanced first-principles
calculations. Electrons localize spontaneously in Ti 3dxy levels within a thin (& 2 nm) interface-adjacent SrTiO3 region for ns lower than a threshold value nc 1014 cm 2. For ns >nc a portion of charge flows into Ti 3dxz-dyz levels extending farther from the interface. This intrinsic confinement can be attributed to the interface-induced symmetry breaking and localized nature of Ti 3d t2g states. The sheet carrier density directly controls the binding energy and the spatial extension of the conductive region. A direct, quantitative relation of these quantities with ns is provided.